On Codex Prompt Engineering for OCL Generation: An Empirical Study

The Object Constraint Language (OCL) is a declarative language that adds constraints and object query expressions to MOF models. Despite its potential to provide precision and conciseness to UML models, the unfamiliar syntax of OCL has hindered its adoption. Recent advancements in LLMs, such as GPT-3, have shown their capability in many NLP tasks, including semantic parsing and text generation. Codex, a GPT-3 descendant, has been fine-tuned on publicly available code from GitHub and can generate code in many programming languages. We investigate the reliability of OCL constraints generated by Codex from natural language specifications. To achieve this, we compiled a dataset of 15 UML models and 168 specifications and crafted a prompt template with slots to populate with UML information and the target task, using both zero- and few-shot learning methods. By measuring the syntactic validity and execution accuracy metrics of the generated OCL constraints, we found that enriching the prompts with UML information and enabling few-shot learning increases the reliability of the generated OCL constraints. Furthermore, the results reveal a close similarity based on sentence embedding between the generated OCL constraints and the human-written ones in the ground truth, implying a level of clarity and understandability in the generated OCL constraints by Codex.